1. Field of the Invention
The systems and methods of this invention relate to direct electrical stimulation of nerve tissue in the spinal cord or spinal column for treatment of pain due to a variety of medical conditions. Specifically, the present invention relates to methods and apparatus for applying such stimulation without the use of conventional lead/electrode systems.
2. Description of the Background Art
Electrical stimulation of spinal nerve roots, the spinal cord, and/or other nerve bundles in the region of the spine, for the purpose of chronic pain management, has been actively practiced since the 1960s. Application of an electrical field to nerve tissue in the spine (i.e., spinal nerve roots and spinal cord bundles) is known to effectively interfere with the transmission of pain signals to the brain. These applications are done today both with externally applied devices and implanted devices. Applying specific electrical pulses to spinal nervous tissue or to peripheral nerve fibers that corresponds to regions of the body afflicted with chronic pain can induce paresthesia, or a subjective sensation of numbness or tingling, or can in effect block pain transmission to the brain from the pain-afflicted regions. Depending on the individual patient, paresthesia can effectively “mask” certain pain sensations to the brain. Treatment regimens and targeted spinal locations are known in related art through use of current, common stimulation devices and methods. Commonly implanted devices for spinal nerve stimulation are made by such companies as Medtronic, Advanced Neuromodulation Systems, Advanced Bionics, and others.
The spine is an anatomical structure that consists of bones (vertebrae), cartilage (discs), and the spinal cord (a nervous system structure that generally bundles or collects various nerves connecting peripheral areas of the body to the brain). As illustrated in FIG. 1 the spine is divided into five regions: (i) cervical (neck), (ii) thoracic (mid-back), (iii) lumbar (lower back), (iv) sacrum, and (v) coccyx (tailbone). The peripheral nervous system refers to the cervical, thoracic, lumbar, and sacral nerve trunks leading away from the spine to all regions of the body. The peripheral nervous system also includes cranial nerves. Pain signals travel between the brain and to other regions of the body using this network of nerves that all travel along the spine as part of the spinal cord.
Transcutaneous electrical nerve stimulation (TENS) is a well known medical treatment used primarily for symptomatic relief and management of chronic intractable pain and as an adjunctive treatment in the management of post surgical and post traumatic acute pain. TENS involves the application of electrical pulses to the skin of a patient, which pulses are generally of a low frequency and are intended to affect the nervous system in such a way as to suppress the sensation of pain, in the area that the electrodes are applied. This typically would be indicated for use in acute or chronic injury or otherwise used as a protective mechanism against pain. Typically, two electrodes are secured to the skin at appropriately selected locations. Mild electrical impulses are then passed into the skin through the electrodes to interact with the nerves lying thereunder. As a symptomatic treatment, TENS has proven to effectively reduce both chronic and acute pain of patients.
Spinal Cord Stimulation (SCS) generally refers to treatments for a variety of medical conditions that apply electrical stimulation directly on nerves, nerve roots, nerve bundles, tissue or regions of the spine. Currently available stimulator systems for SCS are fully implanted electronic devices placed subcutaneously under the skin and connected via insulated metal lead(s) to electrodes which are invasively inserted into or onto the nerves or close to the nerves or spinal cord region. A commonly implanted SCS system contains a battery to power the system. Some implanted SCS systems use an RF wireless connection instead of a battery to power the implanted device. In these RF systems, a receiver device is implanted subcutaneously and a transmitter is worn on the outside of the body. The antenna are tuned to each other and aligned such that control information and power is transmitted to the receiver, which then directs the electrical impulses to the electrodes through the leads. The external transmitter contains batteries to power the transmission. All systems have the capability to externally adjust settings of the implanted system through a programming device.
In SCS and TENS systems, electrical energy is delivered through lead wires to the electrodes. For SCS, implanted electrodes are positioned external to a patient's dura layer (epidural), a structure that surrounds the spinal cord. SCS uses the implanted electrodes to deliver a variety of stimulation modalities with the electric pulse waveform defined by a plurality of variables, including: pulse width, pulse frequency (Hz) or duty cycle, amplitude (V), and sometimes waveform shape (e.g. mono-phasic or bi-phasic).
SCS is used for treatment of headache, migraine headache, or facial pain by stimulating spinal cord including the trigeminal ganglion or ganglia, a trigeminal nerve(s), a branch(es) of a trigeminal nerve(s) (e.g., an ophthalmic nerve(s), a maxillary nerve(s), and/or a mandibular nerve(s)), or a branch(es) of any of these neural structures.
SCS is used for the treatment of chronic pelvic pain due to such conditions as lumbosacral radiculitis, lumbosacral radiculopathy, lumbosacral plexitis, lumbosacral plexopathy, vulvadynia, coccygodynia, peripheral neuritis, and peripheral neuropathy, by applying stimulation to the epidural space of the sacrum on or near selected sacral nerve roots.
SCS is used for chronic pain associated with injury to the spine such as herniated discs or compression fractures. SCS is also used for treating severe chronic pain of a nonspecific origin. Stimulation of nerve tissue in a variety of spinal areas is known to reduce symptoms and enhance the quality of life in patients with chronic pain.
As described above, TENS and SCS devices are battery-powered electronic devices either used transcutaneously (TENS) or implanted (SCS) and connected via insulated metal lead(s) to electrodes which are either placed on the skin (TENS) over the spine or implanted into the dura or epidural layer of the spine (SCS). The implanted electrodes for SCS are positioned on leads that are placed percutaneously, through needle punctures, or through minimally invasive surgical procedures such laminectomy methods, or through direct surgical access to position the electrodes into epidural regions of the spine. Multiple electrodes typically between 4 and 16 are available on the lead and are positioned in the region that is targeted for electrical stimulation. The implanted leads are then subcutaneously tunneled to the pulse generator (also referred to as a controller) that is implanted in a subcutaneous pocket. The use of these lead wires is associated with significant problems such as complications due to infection, lead failure, lead migration, and electrode/lead dislodgement.
Many attempts to overcome the complications and limitations imposed by the use of electrical leads have been reported. For example, self-contained implantable microstimulators and remotely powered microstimulators have been described; however each approach suffers from some significant limitation. A self-contained microstimulator must incorporate a battery or some other power supply; this imposes constraints on size, device lifetime, available stimulation energy, or all three. Due to high use or high energy requirements of the therapeutic stimulation some SCS devices contain recharageable batteries or are powered remotely with an RF coupling to the controller.
For leadless solutions in other similar stimulation applications, remotely powered devices have previously utilized either radiofrequency (RF) or electromagnetic transformer power transmission. RF energy transmission, unless the transmitting and receiving antennae are placed in close proximity, suffers from inefficiency and limited safe power transfer capabilities, limiting its usefulness in applications where recharging or stimulation must be accomplished at any significant depth (>1-2 cm) within the body, in particular where it is desired to permanently implant both the transmitter and receiver-stimulator. Electromagnetic coupling can more efficiently transfer electrical power, and can safely transfer higher levels of power (devices with capacity in excess of 20 Watts have been produced) but again relies on close proximity between transmitting and receiving coils, or the utilization of relatively large devices for deeper (5-8 cm maximum) implantation.
The methods and apparatus of the current invention utilize vibrational energy, particularly at ultrasonic frequencies, to overcome many of the limitations of currently known solutions for SCS and TENS, by achieving a spinal cord stimulation capability without the use of leads connected to a stimulation controller/pulse generator.
The following patents, all of which are incorporated in this disclosure in their entirety, describe various aspects of using electrical stimulation for achieving various beneficial effects. U.S. Pat. No. 3,835,833 titled “Method for Obtaining Neurophysiological Effects” by Limoge describes delivery and parameters for electrical stimulation in a TENS stimulation system. U.S. Pat. No. 4,690,144 titled “Wireless Transcutaneous Electrical Tissue Stimulator” by Rise et al. also describes delivery, systems, and application parameters for a TENS stimulation system. U.S. Pat. No. 6,735,475 titled “Fully implantable miniature neurostimulator for stimulation as a therapy for headache and/or facial pain” by Whitehurst et al. describes an implantable microstimulator used for treatment of pain in peripheral nerves generally in the skull or the cervical regions of the spine. U.S. Pat. No. 6,748,276 titled “Neuromodulation therapy system” by Daignault et al. describes an implantable SCS system that uses an external RF communication to adjust delivery of therapy. U.S. Pat. No. 6,027,456 titled “Apparatus and method for positioning spinal cord stimulation leads” by Feler et al. describes approaches to the implantation of leads into the dorsal column of a patient. U.S. Pat. No. 5,938,690 titled “Pain management system and method” by Law et al. describes methods for determining and optimizing treatment parameters and regimens for by mapping patient responses to test stimulation patterns. U.S. Pat. No. 6,002,965 titled “Epidural nerve root stimulation” by Feler et al. describes treating pelvic pain by application of stimulation in the sacral and lumbar regions of the spine. U.S. Pat. No. 5,405,367 titled “Structure and Method of Manufacture of an Implantable Microstimulator” by Schulman et al. describes an implantable microstimulator used generally for stimulation of tissue. U.S. Pat. No. 6,037,704 titled “Ultrasonic Power Communication System” by Welle describes the use of ultrasound energy transfer from a transmitter to a receiver for purposes of powering a sensor or actuator without being connected by a lead/wire. U.S. Pat. No. 6,366,816 titled “Electronic Stimulation Equipment with Wireless Satellite Units” by Marchesi describes a tissue stimulation system based on a wireless radio transmission requiring the charging of a battery at the receiver and separate command signals used to control the delivery of stimulation. German patent application DE4330680A1 titled “Device for Electrical Stimulation of Cells within a Living Human or Animal” by Zwicker describes a general approach to power transfer using acoustic energy for tissue stimulation.